How do I open a file as root in TextEdit on Lion?

You can open up a textedit instance as root by entering the full path to the actual executable :

sudo -b "/Applications/Textedit.app/Contents/MacOS/TextEdit"

Once your root instance is open you could browse to the file you need or do this from the command line :

sudo su - root -c "open -e /etc/apache2/httpd.conf"

BBEdit is the free tool to do this in 2019 and it replaces all functionality of TextErangler and you can download it from the App Store and the developer web site.

TextEdit isn't really the right tool for editing config files -- use TextWrangler instead. It's free, has built-in capability to edit files with root access from an admin account, as well as things like opening invisible files and directories easily editing files over SFTP, etc.

Here's a way to avoid running TextEdit as root:

EDITOR='open -Wne' sudo -e /etc/apache2/httpd.conf

You will need to quit the copy of TextEdit after editing the file.

sudo -e, sometimes known as sudoedit but not on OS X, makes a temporary copy of the file with write permission for the current user, invokes an editor on it in the usual Unix fashion, and then copies it back.

The options to open: -W waits for TextEdit to quit, so sudo knows when to copy the file back. -n ensures that it's waiting on a separate instance of TextEdit, not one you already have open which you might not want to quit. You can also substitute -t instead of -e if you have a favorite text editor other than TextEdit.

If you already have an EDITOR variable set to use a graphical editor with its own wait-capable command line tool (such as TextMate or BBEdit), then you don't need any of these tricks and can just use sudo -e <file> directly.